<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        * {
            margin:0;
            padding:0;
            box-sizing:border-box;
        }
        .box {
            position:relative;
            height: 2.5rem;
        
        }
        .box::after {
            content:'';
            position:absolute;
            bottom:0;
            left:0;
            right:0;
            height:1px;
            background-color: black;
            transform-origin:0 100%; /*?*/
            transform:scaleY(50%);
        }
    </style>
</head>
<body>
    <div class="box">1</div>
    <div class="box">1</div>
    <div class="box">1</div>
</body>
</html>